Reciprocating engine

ABSTRACT

A reciprocating engine comprises: a piston ring; a piston ring which defines an annular gas chamber in cooperation with the piston ring and which is adjacent to the piston ring such that a pressure-receiving area of a side surface of a piston in the annular gas chamber becomes greater on a thrust side than on a counter-thrust side of the piston; and gas passages for allowing the annular gas chamber to communicate with the combustion chamber.

TECHNICAL FIELD

The present invention relates to a reciprocating engine for use in anautomobile or the like.

BACKGROUND ART

As a reciprocating engine of this type, a reciprocating engine has beenproposed in JP-A-5-180069 in which, in order to reduce slidingfrictional resistance between a side surface of a piston and an innersurface of a cylinder which increases as a connecting rod is inclined inan explosion stroke (combustion stroke), a second piston ring (secondring) adjacent to a first piston ring (top ring) is inclined withrespect to the first piston ring, and a combustion chamber and anannular gas chamber between the first and second piston rings arecommunicated through a gas passage. In such a reciprocating engine, thesupport of the piston (gas-pressure support) on the thrust sideoccurring on the basis of the gas pressure of the annular gas chamber isincreased by tilting the second piston ring, so as to reduce the slidingfrictional resistance between the inner surface of the cylinder, on theone hand, and the side surfaces of the piston rings and the side surfaceof the piston, on the other hand, due to the lateral pressure of thepiston.

In addition, as another reciprocating engine of this type, areciprocating engine has been proposed in JP-A-5-5459 in which, in orderto reduce the sliding frictional resistance between the inner surface ofthe cylinder and the side surface of the piston in the reciprocatingmotion of the piston, a second piston ring (second ring) adjacent to afirst piston ring (top ring) is inclined with respect to the firstpiston ring. In such a reciprocating engine, the lateral pressure on thethrust side occurring on the basis of combustion gases is increased bytilting the second piston ring, so as to reduce the thrust-side slidingfrictional resistance between the inner surface of the cylinder, on theone hand, and the side surfaces of the piston rings and the side surfaceof the piston, on the other hand, which can increase on the basis of thegas pressure and the like of the combustion gases in the combustionchamber with respect to the piston.

Incidentally, in such a reciprocating engine, if the second piston ringis inclined to gas-pressure support the piston by generating gaspressure which resists the lateral pressure of the piston, the volume onthe thrust side of the annular gas chamber defined by the first andsecond piston rings becomes greater than the volume on thecounter-thrust side thereof. Therefore, a required amount of combustiongases in the combustion chamber cannot be speedily introduced into theannular gas chamber through a single gas passage. Hence, it is difficultto substantially reduce the sliding frictional resistance between thecylinder, on the one hand, and the piston rings and the side surface ofthe piston, on the other hand, by generating desired supporting force.In a case where the second piston ring is inclined greatly or in a casewhere the period of communication between the combustion chamber and theannular gas chamber per reciprocating motion becomes short due to thehigh-speed rotation of the reciprocating engine, it can become even moredifficult to introduce a required amount of combustion gases in thecombustion chamber speedily into the annular gas chamber.

In addition, with the above-described other reciprocating engine, if thesecond piston ring is inclined greatly so as to generate large lateralpressure on the thrust side, there is a possibility that the inclinedsecond piston ring interferes with an oil ring. Accordingly, it isdifficult to substantially reduce the sliding frictional resistancebetween the cylinder, on the one hand, and the piston rings and the sidesurface of the piston by generating desired lateral pressure.

The present invention has been devised in view of the above-describedaspects, and its object is to provide a reciprocating engine which iscapable of speedily introducing a necessary amount of gases in thecombustion chamber into and causing it to act in the annular gas chamberwith necessary force during a starting period of the fall of the pistonin the explosion stroke and of generating a desired gas-pressuresupporting force, thereby making it possible to substantially reduce thesliding frictional resistance between the cylinder, on the one hand, andthe piston rings and the side surface of the piston, on the other hand.

Another object of the present invention is to provide a reciprocatingengine which is capable of eliminating the interference of the pistonring with the oil ring and of generating the desire lateral pressure,thereby making it possible to substantially reduce the slidingfrictional resistance between the cylinder, on the one hand, and thepiston rings and the side surface of the piston, on the other hand.

DISCLOSURE OF THE INVENTION

The reciprocating engine in accordance with a first aspect of theinvention comprises: a first piston ring adjacent to a top surface of apiston defining a combustion chamber; a second piston ring which definesan annular gas chamber in cooperation with the first piston ring andwhich is adjacent to the first piston ring such that apressure-receiving area of a side surface of the piston in the annulargas chamber becomes greater on a thrust side than on a counter-thrustside; and a plurality of gas passages which are disposed in an innersurface of a cylinder in such a manner as to be juxtaposed in acircumferential direction of the inner surface of the cylinder and whichallow the annular gas chamber to communicate with the combustion chamberon the thrust side.

According to the reciprocating engine in accordance with the firstaspect, since the above-described construction is provided, a necessaryamount of gases in the combustion chamber can be speedily introducedinto and causing it to act in the annular gas chamber during a startingperiod of the fall of the piston in the explosion stroke, for example,through the plurality of gas passages which are disposed in the innersurface of the cylinder in such a manner as to be juxtaposed in thecircumferential direction of the inner surface of the cylinder. Adesired supporting force can be generated on the basis of the gaspressure within the annular gas chamber thus obtained so as togas-pressure support the piston from the inner surface of the cylinder,thereby making it possible to substantially reduce the slidingfrictional resistance between the cylinder, on the one hand, and thepiston rings and the side surface of the piston, on the other hand.

Regarding the reciprocating engine in accordance with a second aspect ofthe invention, in the reciprocating engine in accordance with the firstaspect, the plurality of gas passages respectively have recessedportions which are disposed in the inner surface of the cylinder atpositions for allowing the annular gas chamber to communicate with thecombustion chamber when the piston is at a top dead center or during astarting period of the fall from the top dead center.

According to the reciprocating engine in accordance with the secondaspect, since the above-described construction is provided, thecombustion gases can be forcibly introduced into and caused to act inthe annular gas chamber extensively and uniformly through the pluralityof recessed portions during the starting period of the fall of thepiston from the top dead center in the explosion stroke, for example.Accordingly, it is possible to increase the gas pressure within theannular gas chamber, and the piston can be lowered (forwardly moved)while this gas pressure is being held. Particularly in the explosionstroke, the piston can be suitably gas-pressure supported in oppositionto the lateral pressure of the piston.

Regarding the reciprocating engine in accordance with a third aspect ofthe invention, in the reciprocating engine in accordance with the secondaspect, the plurality of recessed portions are adapted to allow only theannular gas chamber to respectively communicate with the combustionchamber.

Regarding the reciprocating engine in accordance with a fourth aspect ofthe invention, in the reciprocating engine in accordance with the secondor third aspect, the plurality of gas passages are disposed in the innersurface of the cylinder at positions for allowing the annular gaschamber to communicate with the combustion chamber during the startingperiod of the fall of the piston from the top dead center.

Regarding the reciprocating engine in accordance with a fifth aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to fourth aspects, at least one of the recessed portions isdisposed in the inner surface of the cylinder at a position for allowingthe annular gas chamber to communicate with the combustion chamber whenthe piston is positioned at the top dead center.

Regarding the reciprocating engine in accordance with a sixth aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to fifth aspects, the at least one of the recessed portionsis disposed in such a manner as to be located further away from acylinder head than other ones of the recessed portions concerning areciprocating direction.

According to the reciprocating engine in accordance with any one of thefourth to sixth aspects, since the above-described construction isprovided, the combustion gases can be sufficiently introduced from thecombustion chamber into the annular gas chamber over a long period oftime.

Regarding the reciprocating engine in accordance with a seventh aspectof the invention, in the reciprocating engine in accordance with any oneof the second to sixth aspects, the at least one of the recessedportions which is located most away from a counter-thrust-side portionof the piston is disposed further away from the cylinder head than theother ones of the recessed portions concerning the reciprocatingdirection.

Regarding the reciprocating engine in accordance with an eighth aspectof the invention, in the reciprocating engine in accordance with any oneof the second to seventh aspects, a center portion of an opening planeof a space defined by the at least one of the recessed portions isdisposed in such a manner as to oppose a center portion of the pistonconcerning a direction which is perpendicular to the reciprocatingdirection and an axial direction of a piston pin for coupling the pistonand a connecting rod.

According to the reciprocating engine in accordance with the seventh oreighth aspect, since the above-described construction is provided, thecombustion gases can be extensively introduced into and caused to act inthe thrust-side portion of the annular gas chamber whose volume isgreater than the counter-thrust-side portion of the annular gas chamber.Accordingly, the gas pressure within the annular gas chamber can beincreased speedily.

Regarding the reciprocating engine in accordance with a ninth aspect ofthe invention, in the reciprocating engine in accordance with the sixthor seventh aspect, a portion located on a cylinder head side in acontiguous portion, which is contiguous to the cylinder inner surface ofthe recessed portion disposed further away from the cylinder head, isdisposed closer to the cylinder head side than portions of contiguousportions contiguous to the cylinder inner surface in the other ones ofthe recessed portions and opposing in the reciprocating direction theportions thereof located on the cylinder head side.

Regarding the reciprocating engine in accordance-with a 10th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to ninth aspects, one portions of the opening planes of thespaces respectively defined by the plurality of recessed portions arerespectively positioned on a line extending in a circumferentialdirection.

According to the reciprocating engine in accordance with the ninth or10th aspect, since the above-described construction is provided, thecombustion gases can be introduced into the annular gas chamber from thecombustion chamber through the plurality of recessed portions and causedto act therein uniformly over a long period of time.

Regarding the reciprocating engine in accordance with an 11th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 10th aspects, there are provided a pair of recessedportions opposing each other concerning the axial direction of thepiston pin for coupling the piston and the connecting rod, and adistance from the cylinder head to one of the recessed portions in thereciprocating direction and a distance from the cylinder head to theother one of the recessed portions in the reciprocating direction aremutually equal.

According to the reciprocating engine in accordance with the 11thaspect, since the above-described construction is provided, thecommunication between the combustion chamber and the annular gas chamberthrough the pair of recessed portions can be started or terminatedsimultaneously. Thus, the compressed gases or combustion gases can bemore speedily introduced into and caused to act in the annular gaschamber.

Regarding the reciprocating engine in accordance with a 12th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 11th aspects, the plurality of recessed portionsrespectively have partially concave spherical surfaces.

According to the reciprocating engine in accordance with the 12thaspect, since the above-described construction is provided, resistanceis not encountered in the influx of the combustion gases, and uniformand satisfactory introduction and action can be obtained.

Regarding the reciprocating engine in accordance with a 13th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 12th aspects, an intersection angle between a lineextending in the reciprocating direction and a tangential line to thecontiguous portion contiguous to the cylinder inner surface in the atleast one of the recessed portions is an obtuse angle.

Regarding the reciprocating engine in accordance with a 14th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 13th aspects, tangential lines to both portions opposingeach other in the reciprocating direction in the contiguous portioncontiguous to the cylinder inner surface in the at least one of therecessed portions intersect each other at a position located furtheraway from the piston than the both portions.

According to the reciprocating engine in accordance with the 13 or 14thaspect, since the above-described construction is provided, introductionand action of the combustion gases are effected extensively anduniformly.

Regarding the reciprocating engine in accordance with a 15th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 12th aspects, a line extending in the reciprocatingdirection and a tangential line to the contiguous portion contiguous tothe cylinder inner surface in the at least one of the recessed portionsare perpendicular to each other.

Regarding the reciprocating engine in accordance with a 16th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 15th aspects, the at least one of the recessed portionshas a depth different from that of the recessed portion adjacent to thatrecessed portion in the circumferential direction.

Regarding the reciprocating engine in accordance with a 17th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 16th aspects, the at least one of the recessed portions isdeeper than the other ones of the recessed portions located on thecounter-thrust side relative to the recessed portion concerning thedirection which is perpendicular to the reciprocating direction and theaxial direction of the piston pin for coupling the piston and theconnecting rod.

Regarding the reciprocating engine in accordance with an 18th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 17th aspects, the at least one of the recessed portionshas a depth equal to that of the recessed portion adjacent to thatrecessed portion in the circumferential direction.

According to the reciprocating engine in accordance with any one of the16th to 18th aspects, since the above-described construction isprovided, the state of communication between the combustion chamber andthe annular gas chamber through the recessed portions can be adjustedappropriately. Here, as the plurality of recessed portions are disposedin the inner surface of the cylinder by being respectively designed inconnection with their curvatures and depths, it is possible to moresatisfactorily adjust the state of communication between the combustionchamber and the annular gas chamber through the recessed portions.

Regarding the reciprocating engine in accordance with a 19th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 18th aspects, there are provided a pair of recessedportions opposing each other concerning the axial direction of thepiston pin for coupling the piston and the connecting rod, and anintersection angle between a line extending in the axial direction and aline connecting the center portion of the piston and the center portionof the opening plane of the space defined by the one of the recessedportions and an intersection angle between the line extending in theaxial direction and a line connecting the center portion of the pistonand the center portion of the opening plane of the space defined by theother one of the recessed portions are mutually equal.

Regarding the reciprocating engine in accordance with a 20th aspect ofthe invention, in the reciprocating engine in accordance with the 19thaspect, the pair of recessed portions have mutually similar shapes.

According to the reciprocating engine in accordance with the 19th or20th aspect, since the above-described construction is provided, thecombustion gases can be uniformly introduced into and caused to act inone side and the other side of the annular gas chamber concerning theaxial direction of the coupling shaft.

Regarding the reciprocating engine in accordance with a 21st aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 20th aspects, an interval between the both portionsopposing each other in the reciprocating direction in each of thecontiguous portions of the plurality of recessed portions contiguous tothe inner surface of the cylinder is greater than a thickness of thefirst piston ring.

Regarding the reciprocating engine in accordance with a 22nd aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 21st aspects, an interval between the both portionsopposing each other in the reciprocating direction in each of thecontiguous portions of the plurality of recessed portions contiguous tothe inner surface of the cylinder is shorter than a distance in thereciprocating direction from a thrust-side portion of a defining surfaceof the first piston ring defining the annular gas chamber to athrust-side portion of a defining surface of the second piston ringdefining the annular gas chamber.

Regarding the reciprocating engine in accordance with a 23rd aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 22nd aspects, the opening plane of the space defined bythe at least one of the recessed portions has a diameter different fromthe opening plane of the space defined by the other one of the recessedportions.

Regarding the reciprocating engine in accordance with a 24th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 23rd aspects, the opening plane of the space defined bythe at least one of the recessed portions has a diameter longer than theopening plane of the space defined by the recessed portion locatedcloser to the counter-thrust side relative to the recessed portionconcerning the reciprocating direction and the axial direction of thepiston pin for coupling the piston and the connecting rod.

Regarding the reciprocating engine in accordance with a 25th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 24th aspects, there are provided a pair of recessedportions opposing each other concerning the axial direction of thepiston pin for coupling the piston and the connecting rod, and thediameter of the opening plane of the space defined by each of the pairof recessed portions and the diameter of the opening plane of the spacedefined by another recessed portion adjacent to the pair of recessedportions in the circumferential direction are mutually different.

Regarding the reciprocating engine in accordance with a 26th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 25th aspects, the opening plane of the space defined bythe at least one of the recessed portions has a diameter equal to thatof the opening plane of the space defined by another one of the recessedportions.

According to the reciprocating engine in accordance with any one of the23rd to 26th aspects, since the above-described construction isprovided, the state of communication between the combustion chamber andthe annular gas chamber through the recessed portions as well as theorder of starting or termination of the communication can be adjustedappropriately.

Regarding the reciprocating engine in accordance with a 27th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe first to 26th aspects, the defining surface the first piston ringdefining the annular gas chamber is disposed so as to be parallel to aplane perpendicular to the reciprocating direction.

Regarding the reciprocating engine in accordance with a 28th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe second to 27th aspects, the diameter of the opening plane of thespace defined by the at least one of the recessed portions is greaterthan a depth of that recessed portion.

Regarding the reciprocating engine in accordance with a 29th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe first to 28th aspects, the piston ring is disposed in such a manneras to be inclined with respect to the reciprocating direction.

Regarding the reciprocating engine in accordance with a 30th aspect ofthe invention, the reciprocating engine in accordance with any one ofthe first to 29th aspects further comprises an oil ring disposed on thepiston in face-to-face relation to the first piston ring with the secondpiston ring located therebetween, and a thrust-side portion of the oilring is located further away from the first piston ring than a portionof the oil ring opposing the piston pin for coupling the piston and theconnecting rod concerning the reciprocating direction.

According to the reciprocating engine in accordance with the 30thaspect, since the above-described construction is provided, the oil ringcan be disposed by being spaced away from the first piston ring withoutinterfering with the coupling shaft for coupling the piston and theconnecting rod, and the second piston ring can be disposed by beingspaced away from the first piston ring particularly on the thrust sidewithout interfering with the oil ring. Here, with the reciprocatingengine, even in a case where the second piston ring together with theoil ring is inclined greatly with respect to the reciprocatingdirection, the combustion gases in an amount sufficient to gas float thepiston can be thoroughly and speedily introduced into and caused to actin the annular gas chamber from the combustion chamber through theabove-described plurality of gas passages.

Regarding the reciprocating engine in accordance with a 31st aspect ofthe invention, in the reciprocating engine in accordance with the 30thaspect, the thrust-side portion of the oil ring is located further awayfrom the first piston ring than a counter-thrust-side portion of the oilring.

Regarding the reciprocating engine in accordance with a 32nd aspect ofthe invention, the reciprocating engine in accordance with the 29thaspect further comprises an oil ring disposed on the piston inface-to-face relation to the first piston ring with the second pistonring located therebetween, and the oil ring is disposed in such a manneras to be inclined with respect to the reciprocating direction.

Regarding the reciprocating engine in accordance with a 33rd aspect ofthe invention, in the reciprocating engine in accordance with the 32ndaspect, the oil ring and the second piston ring are disposed in such amanner as to be inclined with respect to the reciprocating directionwith mutually equal angles.

Regarding the reciprocating engine in accordance with a 34th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe first to 33rd aspects, the piston pin for coupling the piston andthe connecting rod are off-centered toward the counter-thrust side.

The reciprocating engine in accordance with a 35th aspect of theinvention comprises: a first piston ring adjacent to a top surface of apiston defining a combustion chamber; a second piston ring which definesan annular gas chamber in cooperation with the first piston ring andwhich is adjacent to the first piston ring such that apressure-receiving area of a side surface of the piston in the annulargas chamber becomes greater on another swinging side surface portionopposing one swinging side surface portion of the piston than on the oneswinging side surface portion; an oil ring which is located further awayfrom the first piston ring on the other swinging side surface portionside than on a substantially intermediate portion side between the oneswinging side surface portion and the other swinging side surfaceportion; and a gas passage formed in at least one of the piston and aninner surface of a cylinder and adapted to allow the annular gas chamberto communicate with the combustion chamber.

According to the reciprocating engine in accordance with the 35thaspect, since the above-described construction is provided, the oil ringcan be disposed by being spaced away from the first piston ring withoutinterfering with the coupling shaft for coupling the piston and theconnecting rod, and the second piston ring can be disposed by beingspaced away from the first piston ring particularly on the otherswinging side surface portion side without interfering with the oilring. Thus, the piston can be floated up (gas floated) from the innersurface of the cylinder by generating desired lateral pressure, therebymaking it possible to substantially reduce the sliding frictionalresistance between the cylinder and the piston rings.

Regarding the reciprocating engine in accordance with a 36th aspect ofthe invention, in the reciprocating engine in accordance with the 35thaspect, the second piston ring is disposed in such a manner as to beinclined with respect to a reciprocating direction of the piston.

Regarding the reciprocating engine in accordance with a 37th aspect ofthe invention, in the reciprocating engine in accordance with the 35thor 36th aspect, the oil ring is disposed in such a manner as to beinclined with respect to a reciprocating direction of the piston.

Regarding the reciprocating engine in accordance with an 38th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe 35th to 37th aspects, the one swinging side surface portion islocated on a counter-thrust side, and the other swinging side surfaceportion is located on a thrust side.

According to the reciprocating engine in accordance with the 38thaspect, since the above-described construction is provided, it ispossible to substantially reduce the sliding frictional resistancebetween the cylinder and the piston rings on the thrust side which canoccur greatly in the combustion stroke, thereby allowing the piston toreciprocate smoothly.

Regarding the reciprocating engine in accordance with a 39th aspect ofthe invention, in the reciprocating engine in accordance with any one ofthe 35th to 38th aspects, the gas passage is constituted by a recessedportion which is disposed in the inner surface of the cylinder at aposition for allowing the annular gas chamber to communicate with thecombustion chamber when the piston is positioned at a top dead center.

The reciprocating engine in accordance with the above-described aspectsmay be a four-cycle gasoline engine or a diesel engine, and eitherengine is capable of suitably demonstrating the advantages based on thepresent invention.

According to the present invention, it is possible to provide areciprocating engine which is capable of speedily introducing anecessary amount of gases in the combustion chamber into and causing itto act in the annular gas chamber with necessary force during a startingperiod of the fall of the piston in the explosion stroke and ofgenerating a desired gas-pressure supporting force, thereby making itpossible to substantially reduce the sliding frictional resistancebetween the cylinder, on the one hand, and the piston rings and the sidesurface of the piston, on the other hand.

In addition, according to the present invention, it is possible toprovide a reciprocating engine which is capable of eliminating theinterference of the piston ring with the oil ring and of generating thedesire lateral pressure, thereby making it possible to substantiallyreduce the sliding frictional resistance between the cylinder, on theone hand, and the piston rings and the side surface of the piston, onthe other hand.

Hereafter, a more detailed description will be given of the mode forcarrying out the invention on the basis of the preferred embodimentsillustrated in the drawings. It should be noted that the invention isnot limited to these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory vertical cross-sectional view of an embodimentof the invention;

FIG. 2 is an explanatory cross-sectional view, taken along line II-II,of the embodiment shown in FIG. 7;

FIG. 3 is an explanatory cross-sectional view, taken along line III-III,of the embodiment shown in FIG. 7;

FIG. 4 is an explanatory enlarged vertical cross-sectional view mainlyof a recessed portion of the embodiment shown in FIG. 1;

FIG. 5 is a diagram explaining the operation of the embodiment shown inFIG. 1;

FIG. 6 is a diagram explaining the operation of the embodiment shown inFIG. 1;

FIG. 7 is a diagram explaining the operation of the embodiment shown inFIG. 1;

FIGS. 8(a), 8(b), and 8(c) are partially enlarged diagrams explainingthe operation of the embodiment shown in FIG. 1;

FIG. 9 is an explanatory diagram of another embodiment of the invention;

FIG. 10 is an explanatory diagram of still another embodiment of theinvention;

FIG. 11 is an explanatory diagram of a further embodiment of theinvention;

FIG. 12 is an explanatory vertical cross-sectional view of a stillfurther embodiment of the invention;

FIG. 13 is an explanatory vertical cross-sectional view of a furtherembodiment of the invention; and

FIG. 14 is an explanatory partial plan view of the further embodimentshown in FIG. 13.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIGS. 1 to 8, a four-cycle gasoline engine 1 serving as areciprocating engine in accordance with this embodiment is comprised ofa piston ring (top ring) 5 adjacent to a top surface (head end face) 4of a piston 3 defining a combustion chamber 2; a piston ring 7 whichdefines an annular gas chamber 6 in cooperation with the piston ring 5and which is adjacent to the piston ring 5 such that thepressure-receiving area of a side surface 8 of the piston 3 in theannular gas chamber 6 becomes greater on a thrust side 10 than on acounter-thrust side 9 of the piston 3; a plurality of gas passages 15which are disposed in an inner surface 14 of a cylinder 13 in such amanner as to be juxtaposed in a circumferential direction X of the innersurface 14 of the cylinder 13 and which allow the annular gas chamber 6to communicate with the combustion chamber 2 on the thrust side 10; andan oil ring 16 disposed in such a manner as to oppose the piston ring 5with the piston ring 7 located therebetween in a reciprocating directionY of the piston 3.

Ring grooves, which are disposed in such a manner as to respectivelycorrespond to the piston rings 5 and 7 and the oil ring 16, are formedin the side surface 8 contiguous to the top surface 4 of the piston 3.The piston rings 5 and 7 and the oil ring 16 are respectively fitted inthe ring grooves. The top surface 4 is formed on the piston 3 so as tobe parallel to a plane perpendicular to the reciprocating direction Y.The side surface 8 is formed on the piston 3 so as to be parallel to thereciprocating direction Y.

In this embodiment, a connecting rod 22, which has a small end portion22 a rotatably coupled to the piston 3 through a piston pin 21 and alarge end portion to which a crankshaft is rotatably coupled, isarranged such that its large end portion is disposed more on thecounter-thrust side than its small end portion 22 a when the piston isreciprocated in a direction Y1, as shown in FIGS. 1 and 7.

The cylinder 13 has a cylinder bore (space) 25 defined by its innersurface 14, and the piston 3 is disposed in the cylinder bore 25 suchthat the piston 3 is reciprocatable in the reciprocating direction Y. Acylinder head 13 a is provided with an ignition plug 26, an intake valve27, and an exhaust valve 28. The inner surface 14 is formed in thecylinder 13 so as to be parallel to the reciprocating direction Y.

The piston ring 5 is fitted in the ring groove of the piston 3 such thatthe piston ring 5 is normally parallel to the top surface 4 of thepiston 3 defining the combustion chamber 2. The piston ring 5 has anannular defining surface Sa defining the combustion chamber 2, anannular defining surface 5 b defining the annular gas chamber 6, and asliding side surface 5 c which is contiguous to the annular definingsurfaces 5 a and Sb and slides on the inner surface 14 of the cylinder13. The annular defining surfaces Sa and Sb are disposed so as to beparallel to a plane perpendicular to the reciprocating direction Y. Thesliding side surface Sc is formed on the piston ring S so as to beparallel to the reciprocating direction Y. The piston ring 5 in thisembodiment is formed with a thin wall so as to be able to define thecombustion chamber 2 and the annular gas chamber 6.

The piston ring 7 is fitted in the ring groove of the piston 3 by beinginclined with respect to the reciprocating direction Y so as togradually move away from the piston ring S as viewed in the directionfrom the counter-thrust side 9 toward the thrust side 10. The pistonring 7 has an annular defining surface 7 a disposed on the piston ring 5side and defining the annular gas chamber 6, an annular surface 7 bdisposed on the oil ring 16 side and opposing the annular definingsurface 7 a, and a sliding side surface 7 c which slides on the innersurface 14 of the cylinder 13. The annular defining surface 7 a and theannular surface 7 b are inclined with respect to the reciprocatingdirection Y so as to be located further away from the annular definingsurface 5 b on their portions on the thrust side 10 than on theirportions on the counter-thrust side 9. The distance in the reciprocatingdirection Y from the portion of the annular defining surface 5 b on thethrust side 10 to the portion of the annular defining surface 7 a on thethrust side 10 is longer than the distance in the reciprocatingdirection Y from the portion of the annular defining surface 5 b on thecounter-thrust side 9 to the portion of the annular defining surface 7 aon the counter-thrust side 9.

The annular gas chamber 6 is defined by the side surface 8 of the piston3, the inner surface 14 of the cylinder 13, and the piston rings 5 and7. Here, the volume of the annular gas chamber 6 is large on the thrustside 10 but is small on the counter-thrust side 9 since the piston ring7 is disposed in an inclined manner, as described above.

The oil ring 16 in this embodiment is fitted in the ring groove of thepiston 3 so as to be parallel to the piston ring (top ring) 5. The oilring 16 has an annular surface 16 a on the piston ring 7 side opposingthe annular surface 7 b, an annular surface 16 b on the piston pin 21side opposing the annular surface 16 a in the reciprocating direction Y,and a sliding side surface 16 c which is contiguous to the annularsurfaces 16 a and 16 b and slides on the inner surface 14. The annularsurfaces 16 a and 16 b in this embodiment are disposed so as to beparallel to the plane perpendicular to the reciprocating direction Y.The sliding side surface 16 c is formed on the oil ring 16 so as to beparallel to the reciprocating direction Y.

In this embodiment, the inner surface 14 of the cylinder 13 is providedwith three gas passage 15. The three gas passages 15 respectively haverecessed portions 17 a, 17 b, and 17 c which are disposed in the innersurface 14 of the cylinder 13 at positions for allowing the annular gaschamber 6 to communicate with the combustion chamber 2 when the piston 3is positioned in the vicinity of the top dead center. The recessedportions 17 a, 17 b, and 17 c in this embodiment are respectively formedin the inner surface 14 opposing the side surface 8 so as torespectively allow only the annular gas chamber 6 to communicate withthe combustion chamber 2 simultaneously in a case where the piston 3 ispresent at a position corresponding to approximately 6 degrees toapproximately 37 degrees in terms of the crank angle concerning thereciprocating direction Y.

The recessed portion 17 b is disposed between the recessed portion 17 aand 17 c in the circumferential direction X, and the recessed portions17 a and 17 c are opposed to each other in an axial direction A of thepiston pin 21. The interval between the recessed portions 17 a and 17 bin the circumferential direction X and the interval between the recessedportions 17 b and 17 c in the circumferential direction X aresubstantially equal to each other. The recessed portions 17 a, 17 b, and17 c in this embodiment have shapes substantially similar to each other.In this embodiment, the distance in the reciprocating direction Y fromthe cylinder head 13 a to the recessed portion 17 a, the distance in thereciprocating direction Y from the cylinder head 13 a to the recessedportion 17B, and the distance in the reciprocating direction Y from thecylinder head 13 a to the recessed portion 17C are substantially equalto each other.

A center portion C2 of a circular opening plane 31 b of a space 30 bdefined by the recessed portion 17 b, in this example, is disposed insuch a manner as to oppose a center portion O of the piston 3 concerninga direction Z which is perpendicular to the axial direction A and thereciprocating direction Y, as shown in FIG. 3. The recessed portion 17 bis located further away from the counter-thrust side 9 than the recessedportions 17 a and 17 c.

An intersection angle 35 between a line 80 extending in the axialdirection A and a line 32 connecting the center portion O of the piston3 and a center portion C 1 of an opening plane 31 a of a space 30 adefined by the recessed portion 17 a, and an intersection angle 37between the line 80 and a line 36 connecting the center portion O of thepiston 3 and a center portion C3 of an opening plane 31 c of a space 30c defined by the recessed portion 17 c, are substantially equal to eachother.

The recessed portion 17 a in this embodiment has a partially concavespherical surface 41 a having a contiguous portion 40 a contiguous tothe inner surface 14 of the cylinder 13. The partially concave sphericalsurface 41 a defines the space 30 a having the circular opening plane 31a. The recessed portion 17 b in this embodiment has a partially concavespherical surface 41 b having a contiguous portion 40 b contiguous tothe inner surface 14 of the cylinder 13. The partially concave sphericalsurface 41 b defines the space 30 b having the circular opening plane 31b. The recessed portion 17 c in this embodiment has a partially concavespherical surface 41 c having a contiguous portion 40 c contiguous tothe inner surface 14 of the cylinder 13. The partially concave sphericalsurface 41 c defines the space 30 cb having the circular opening plane31 c. It should be noted that the recessed portions 17 a, 17 b, and 17 cmay respectively have angular surfaces instead of the partially concavespherical surfaces 41 a, 41 b, and 41 c. Further, each of the contiguousportions 40 a, 40 b, and 40 c may be provided with slight chamfering.

The partially concave spherical surfaces 41 a, 41 b, and 41 c in thisembodiment have mutually equal curvatures and depths in the directionperpendicular to the reciprocating direction Y. The circular openingplanes 31 a, 31 b, and 31 c in this embodiment have mutually equaldiameters.

The recessed portion 17 b in this embodiment is provided in the innersurface 14 such that an intersection angle 44 between a tangential line42 to the contiguous portion 40 b and a line 43 extending in thereciprocating direction Y assumes an obtuse angle, as shown in FIG. 4.In this embodiment, the lines 42 tangential to portions 45 and 46 of thecontiguous portion 40 b opposing each other in the reciprocatingdirection Y intersect each other at a point of intersection P at aposition located further away from the piston 3 than the portions 45 and46 in the direction perpendicular to the reciprocating direction Y. Thedistance LI between the portions 45 and 46 in the reciprocatingdirection Y is longer than the distance L2 from the annular definingsurface 5 a to the annular defining surface 5 b in the reciprocatingdirection Y. In other words, the interval between these portions 45 and46 is greater than the thickness of the piston ring 5. As shown in FIG.8(b), the distance Li is shorter than the distance L3 in thereciprocating direction Y from the portion on the thrust side 10 of theannular defining surface 5 b to the portion on the thrust side 10 of theannular defining surface 7 a. The diameter of the opening plane 31 b ofthe space 30 b defined by the recessed portion 17 b is greater than thedepth of that recessed portion 17 b in the direction perpendicular tothe reciprocating direction Y. It should be noted that, in thisembodiment, since the contiguous portions 40 a and 40 c are constructedin the same way as the contiguous portion 40 b, a detailed descriptionthereof will be omitted.

To describe the operation of the reciprocating engine 1 in thisembodiment, in the compression stroke, when the annular defining surface5 b of the piston ring 5 is positioned closer to the cylinder head 13 aside than the portion 46 on the piston pin 21 side of the recessedportion 17 b opposing the portion 45 on the cylinder head 13 a sidethereof while the piston 3 is positioned in the vicinity of the top deadcenter and before it reaches the top dead center, the combustion chamber2 communicates with the annular gas chamber 6 through the recessedportion 17 b, and low-pressure compressed gases start to enter theannular gas chamber 6 from the combustion chamber 2. Here, since thepiston ring 5 is disposed so as to be parallel to the top surface 4, thecombustion chamber 2 is communicated with the annular gas chamber 6 alsothrough the spaces 30 a and 30 c defined by the recessed portions 17 aand 17 c juxtaposed to the recessed portion 17 b in the circumferentialdirection X simultaneously with its communication with the annular gaschamber 6 through the space 30 b. As a result, the low-pressurecompressed gases enter the annular gas chamber 6 from the plurality ofportions on the thrust side 10.

Next, in the explosion stroke (combustion stroke) shown in FIGS. 1, 6,and 8(c), during the starting period of the fall of the piston 3, i.e.,when the piston 3 falls in the vicinity of the top dead center,combustion gases 51 in the combustion chamber 2 are introduced into theannular gas chamber 6 through the recessed portions 17 a, 17 b, and 17c. The gas pressure within the annular gas chamber 6 is increased by thegas pressure of the introduced combustion gases 51, so that the piston 3which is gas-pressure supported on the basis of that gas pressure fallstoward the bottom dead center. Here, a forward moving force directed inthe direction Y1 is imparted to the connecting rod 22 tilted withrespect to the reciprocating direction Y from the piston 3 which isbeing moved forward while being gas-pressure supported by the gaspressure being held in the annular gas chamber 6. Consequently, alateral pressure BI directed toward the thrust side 10 is imparted tothe piston 3. However, in opposition to that lateral pressure B1, asupporting force B2 directed toward the counter-thrust side 9 isimparted to the piston 3 by the gas pressure supplied sufficiently tothe interior of the annular gas chamber 6, thereby gas-pressuresupporting the piston 3. It should be noted that in the case where thepiston 3 is positioned at the top dead center, as shown in FIG. 6, thecommunication between the combustion chamber 2 and the annular gaschamber 6 through the recessed portions 17 a, 17 b, and 17 c is stoppedin this embodiment, as particularly shown in FIG. 8(b), but thecommunication may be allowed.

In the reciprocating engine 1 constructed as described above, since thepiston 3 is brought to the position where the combustion chamber 2 andthe annular gas chamber 6 are communicated through the recessed portions17 a, 17 b, and 17 c during the combustion, the gas pressure which isgenerated through combustion in the combustion chamber 2 in thecombustion stroke is speedily introduced thoroughly into the annular gaschamber 6 through the recessed portions 17 a, 17 b, and 17 c. Uponreceiving the biased pressure within the annular gas chamber 6 on thebasis of this introduced gas pressure, the piston 3 is gas-pressuresupported at the inner surface 14, particularly at the portion on thethrust side 10 of the inner surface 14, in its reciprocating motion. Thepiston 3 which is supported by the gas pressure reciprocates with anextremely low sliding frictional resistance. In addition, in suchreciprocating motion, although the piston 3 tends to be swung(oscillated) within the plane perpendicular to the axial direction Aabout the piston pin 21, this swinging motion is prevented by theaforementioned gas pressure of the annular gas chamber 6. The piston 3can thus be reciprocated with an extremely low sliding frictionalresistance, thereby making it possible to attain an improvement and thelike of the fuel consumption of the reciprocating engine 1.

According to the reciprocating engine 1 of this embodiment, thereciprocating engine 1 is comprised of the piston ring 5 adjacent to thetop surface 4 of the piston 3 defining the combustion chamber 2; thepiston ring 7 which defines the annular gas chamber 6 in cooperationwith the piston ring 5 and which is adjacent to the piston ring 5 suchthat the pressure-receiving area of the side surface 8 of the piston 3in the annular gas chamber 6 becomes greater on the thrust side 10 thanon the counter-thrust side 9; the plurality of gas passages 15 which aredisposed in the inner surface 14 of the cylinder 13 in such a manner asto be juxtaposed in the circumferential direction X of the inner surface14 of the cylinder 13 and which allow the annular gas chamber 6 tocommunicate with the combustion chamber 2 on the thrust side. Therefore,the combustion gases 51 in the combustion chamber 2 can be speedilyintroduced thoroughly into the annular gas chamber 6 through theplurality of gas passages 15. Hence, a desired supporting force can begenerated on the basis of the combustion gases 51 in the annular gaschamber 6 thus introduced and caused to act, and the piston 3 isgas-pressure supported with respect to the inner surface 14. It isthereby possible to substantially reduce the sliding frictionalresistance between the inner surface 14 of the cylinder 13, on the onehand, and the sliding side surface 5 c of the piston ring 5 and the sidesurface 8 of the piston 3, on the other hand. Since the plurality of gaspassages 15 respectively have the recessed portions 17 a, 17 b, and 17 cwhich are disposed in the inner surface 14 at positions for allowing theannular gas chamber 6 to communicate with the combustion chamber 2 whenthe piston 3 is lowered in the vicinity of the top dead center, thecombustion gases 51 can be forcibly introduced into and caused to act inthe annular gas chamber 6 through the recessed portions 17 a, 17 b, and17 c in the vicinity of the top dead center. Furthermore, it is possibleto increase the gas pressure within the annular gas chamber 6, and thepiston 3 can be lowered (forwardly moved) while this gas pressure isbeing held. Particularly in the explosion stroke, the piston 3 can besuitably gas-pressure supported in opposition to the lateral pressure ofthe piston. Since the center portion C2 of the opening plane 31 b of thespace 30 b defined by the recessed portion 17 b is disposed in such amanner as to oppose the center portion O of the piston 3 concerning thedirection Z, the compressed gases can be introduced preceding with theportion on the thrust side 10 of the annular gas chamber 6 whose volumeis greater than the portion on the counter-thrust side 9 of the annulargas chamber 6. Accordingly, the combustion gases 51 can be speedilyintroduced more thoroughly into the annular gas chamber 6 and caused toact. Since the distance from the cylinder head 13 a to the recessedportion 17 a in the reciprocating direction Y and the distance from thecylinder head 13 a to the recessed portion 17 c are mutually equal, thecommunication between the combustion chamber 2 and the annular gaschamber 6 through the pair of recessed portions 17 a and 17 c can bestarted or terminated simultaneously and extensively. Thus, thecombustion gases 51 can be more speedily and extensively introduced intoand caused to act in the annular gas chamber 6. Since the recessedportions 17 a, 17 b, and 17 c respectively have the partially concavespherical surfaces 41 a, 41 b, and 41 c, resistance is not encounteredin the influx of the combustion gases 51, and uniform and satisfactoryintroduction and action can be obtained. Further, the intersection angle44 between the line 43 extending in the reciprocating direction Y andthe tangential line 42 to the contiguous portion 40 b of the partiallyconcave spherical surface 41 b contiguous to the inner surface 14 of therecessed portion 17 b assumes an obtuse angle. Still further, the lines42 tangential to the portions 45 and 46 of the contiguous portion 40 bopposing each other in the reciprocating direction Y intersect eachother at a position located further away from the piston 3 than theportions 45 and 45 in the direction perpendicular to the reciprocatingdirection Y. Furthermore, the recessed portions 17 a and 17 c areconstructed in the same way as the recessed portion 17 b. Therefore, thecombustion gases 51 can be introduced extensively. The recessed portion17 b has a curvature which is mutually equal to the curvatures of therecessed portions 17 a and 17 c adjacent to that recessed portion 17 bin the circumferential direction X. In addition, the recessed portion 17b has a depth equal to the depths of the recessed portions 17 a and 17 cadjacent to that recessed portion 17 b in the circumferential directionX. Therefore, since the recessed portions 17 a, 17 b, and 17 c arerespectively designed in connection with their curvatures and depths andare disposed in the inner surface 14, the combustion chamber 2 and theannular gas chamber 6 can be communicated with each other by means ofthe recessed portions 17 a, 17 b, and 17 c in a similar manner,respectively. The intersection angle 35 between the line 80 extending inthe axial direction A and the line 32 connecting the center portion O ofthe piston 3 and the center portion Cl of the opening plane 31 a of thespace 30 a defined by the recessed portion 17 a, and the intersectionangle 37 between the line 80 and the line 36 connecting the centerportion O of the piston 3 and the center portion C3 of the opening plane31 c of the space 30 c defined by the recessed portion 17 c, aresubstantially equal to each other. Further, the recessed portions 17 aand 17 c have mutually identical shapes. Therefore, the combustion gases51 can be introduced uniformly into one side and the other side of thecombustion chamber 6 concerning the axial direction A. Since the openingplane 31 b of the space 30 b defined by the recessed portion 17 b has adiameter substantially equal to the diameters of the opening planes 31 aand 31 c of the spaces 30 a and 30 c defined by the other recessedportions 17 a and 17 c, the combustion chamber 2 and the annular gaschamber 6 can be communicated in a similar state by the recessedportions 17 a, 17 b, and 17 c, and the communication can besimultaneously started or terminated. Since the annular defining surface5 a is disposed so as to be parallel to the plane perpendicular to thereciprocating direction Y, and the annular defining surface 5 b isdisposed so as to be parallel to the plane perpendicular to thereciprocating direction Y, the communication between the combustionchamber 2 and the annular gas chamber 6 by the recessed portions 17 a,17 b, and 17 c, which are juxtaposed to each other in thecircumferential direction, can be simultaneously started or terminated.

It should be noted that, as shown in FIG. 9, the reciprocating engine 1of this embodiment may have, instead of the recessed portion 17 b, forinstance, a recessed portion 52 which is located most away from theportion on the counter-thrust side 9 of the piston 3 and is disposedfurther away from the cylinder head 13 a than the other recessedportions 17 a and 17 c concerning the reciprocating direction Y. Byvirtue of such a recessed portion 52, the gases can be introduced fromthe portion on the thrust side 10 of the annular gas chamber 6 whosevolume is greater than the portion on the counter-thrust side 9 of theannular gas chamber 6 in advance of the recessed portions 17 a and 17 c.Accordingly, the combustion gases 51 can be introduced more thoroughlyand speedily into the annular gas chamber 6. It should be noted that therecessed portion 52 may be disposed in the inner surface 14 of thecylinder 13 by replacing at least one of the recessed portions 17 a, 17b, and 17 c or in addition to the recessed portions 17 a, 17 b, and 17c. By disposing such a recessed portion 52, the order in which therespective ones of the recessed portions 17 a, 17 b, 17 c, and 52 allowthe combustion chamber 2 and the annular gas chamber 6 to communicatewith each other can be adjusted appropriately. Here, as shown in FIG. 9,the portion 45 located on the cylinder head 13 a side in a contiguousportion 40 d, which is contiguous to the inner surface 14 of therecessed portion 52 disposed further away from the cylinder head 13 a inthe reciprocating direction Y, may be disposed closer to the cylinderhead 13 a side than the portions 46 of the contiguous portions 40 a and40 c opposing in the reciprocating direction Y the portions 45 thereoflocated on the cylinder head 13 a side. Portions of the opening planes31 a, 31 c, and 31 d of the spaces 30 a, 30 c, and 30 d respectivelydefined by the recessed portions 17 a, 17 b, and 17 c may berespectively positioned on a line 53 extending the circumferentialdirection X. In addition, for example, the center portions C1 and C3 ofthe opening planes 31 a and 31 c of the recessed portions 17 a and 17 cmay be positioned on a line 54 passing through the portion 45 of thecontiguous portion 40 d and extending in the circumferential directionX. In the case where the recessed portions 17 a, 17 c, and 52 are thusdisposed, the combustion gases can be introduced continuously into theannular gas chamber 6 from the combustion chamber 2 without interruptionby means of these recessed portions 17 a, 17 c, and 52.

In addition, the reciprocating engine 1 of this embodiment may have twogas passages 15 disposed in the inner surface 14 of the cylinder 13,instead of the three gas passages 15. Further, as shown in FIGS. 10 and11, the reciprocating engine 1 of this embodiment may have more thanthree gas passages (four or five gas passages, etc.) 15. Thus, incorrespondence with the various forms of the reciprocating engine 1, thenumber of the gas passages 15 can be set appropriately such that thecombustion gases 51 can be introduced thoroughly, extensively, andspeedily into the annular gas chamber 6. Here, in the case where, forinstance, four gas passages 15 are provided, as shown in FIG. 10, anintersection angle 64 between the line 80 and a line 60 connecting thecenter portion O of the piston 3 and a center portion C4 of an openingplane 3 le of a space 30 e defined by a recessed portion 56, and anintersection angle 67 between the line 80 and a line 63 connecting thecenter portion O and a center portion C7 of an opening plane 31 h of aspace 30 h defined by a recessed portion 59 opposing the recessedportion 56 in the axial direction A, are preferably substantially equalangles. Meanwhile, an intersection angle 65 between the line 80 and aline 61 connecting the center portion O and a center portion C5 of anopening plane 31 f of a space 30 f defined by a recessed portion 57adjacent to the recessed portion 56 in the circumferential direction X,and an intersection angle 66 between the line 80 and a line 62connecting the center portion O and a center portion C6 of an openingplane 31 g of a space 30 g defined by a recessed portion 58 opposing therecessed portion 57 in the axial direction A and adjacent to therecessed portion 59 in the circumferential direction X, are preferablysubstantially equal angles. In such a case, the combustion gases 51 canbe uniformly introduced into and caused to act in the one side and theother side of the annular gas chamber 6 concerning the axial directionA.

Furthermore, instead of the recessed portions 17 a, 17 b, and 17 c, thereciprocating engine 1 of this embodiment may have the recessed portions56, 57, 58, and 59 whose depths in the direction perpendicular to thereciprocating direction Y are mutually different, as well as a recessedportion 70 opposing the center portion O of the piston 3 in thedirection Z. Preferably, the recessed portion 70 located closest to thethrust side 10 is constructed so as to be deeper than the recessedportions 56, 57, 58, and 59 located on the counter-thrust side 9relative to the recessed portion 70 concerning the direction Z, and therecessed portions 57 and 58 are constructed so as to be deeper than therecessed portions 56 and 59. In addition, the reciprocating engine 1 mayhave the recessed portions 56, 57, 58, and 59 whose curvatures aremutually different. Preferably, the recessed portion 70 located closestto the thrust side 10 has a smaller curvature than the recessed portions56, 57, 58, and 59 located on the counter-thrust side 9 relative to thatrecessed portion 70 concerning the direction Z, and the recessedportions 57 and 58 have smaller curvatures than the recessed portions 56and 59. Furthermore, the radii or diameters of the opening planes 31 e,31 g, 31 f, 31 h, and 31 i of the spaces 30 e, 30 f, 30 g, 30 h, and 30i respectively defined by the recessed portions 56, 57, 58, 59, and 70may be mutually different. Preferably, the opening plane 31 i in therecessed portion 70 located closest to the thrust side 10 has a longerradius or diameter than the opening planes 31 e, 31 f, 31 g, and 31 h,and 31 i in the recessed portions 56, 57, 58, and 59 located on thecounter-thrust side 9 relative to that recessed portion 70 concerningthe direction Z. Meanwhile, the opening planes 31 f and 31 g in therecessed portions 57 and 58 have longer radii or diameters than theopening planes 31 e and 31 h in the recessed portions 56 and 59. Byconstructing the recessed portions 56, 57, 58, 59, and 70 respectivelyhaving the above-described depths, curvatures, and diameters (includingradii and diameters), the state of communication between the combustionchamber 2 and the annular gas chamber 6 as well as the order of startingor termination of the communication can be adjusted appropriately. Asthe recessed portions 56, 57, 58, 59, and 70 are disposed in the innersurface 14 of the cylinder 13 by being respectively designedparticularly in connection with the above-described curvatures anddepths, it is possible to more satisfactorily adjust the state ofcommunication between the combustion chamber 2 and the annular gaschamber 6 through the recessed portions 56, 57, 58, 59, and 70.

Furthermore, as shown in FIG. 12, instead of the oil ring 16, thereciprocating engine 1 of this embodiment may have an oil ring 75 whichis disposed on the piston 3 in face-to-face relation to the piston ring5 with the piston ring 7 disposed therebetween, and which is inclinedwith respect to the reciprocating direction Y such that its portion 71on the thrust side 10 is located further away from the piston ring 5than its portion 72 opposing the piston pin 21 connecting the piston 3and the connecting rod 22 and its portion 73 on the counter-thrust side9 concerning the reciprocating direction Y. In such a case, the pistonring 7 may be inclined with respect to the reciprocating direction Ywith an angle equal to the angle of inclination of the oil ring 75.According to the reciprocating engine 1 having the oil ring 75, the oilring 75 can be disposed by being spaced away from the piston ring 5without interfering with the piston pin 21, and the piston ring 7 can bedisposed by being spaced away from the piston ring 5 particularly on thethrust side 10 without interfering with the oil ring 75. Here, with thereciprocating engine 1, even in a case where the piston ring 7 togetherwith the oil ring 75 is inclined greatly with respect to thereciprocating direction Y, the combustion gases 51 in an amountsufficient to gas-pressure support the piston 3 can be thoroughly andspeedily introduced into and caused to act in the annular gas chamber 6from the combustion chamber 2 through the above-described plurality ofgas passages 15, thereby increasing the gas pressure.

In addition, the reciprocating engine 1 of this embodiment may have apiston pin which is off-centered toward the counter-thrust side 9,instead of the piston pin 21.

It should be noted that, in this embodiment, the plurality of gaspassages 15 respectively have the recessed portions 17 a, 17 b, and 17 cwhich are disposed in the vicinities of the top dead center such thatthe communication between the combustion chamber 2 and the annular gaschamber 6 is temporarily canceled in the case where the piston 3 ispositioned at the top dead center, as shown in FIG. 6. However, insteadof at least one of the recessed portions 17 a, 17 b, and 17 c or inaddition thereto, the plurality of gas passages 15 may have a recessedportion or recessed portions which are disposed so as to allow thecombustion chamber 2 and the annular gas chamber 6 to communicate alsoin the case where the piston 3 is positioned at the top dead center.Furthermore, instead of at least one of the recessed portions 17 a, 17b, and 17 c or in addition thereto, the plurality of gas passages 15 mayhave a recessed portion or recessed portions which are disposed in theinner surface of the cylinder 13 such that the line 43 extending in thereciprocating direction Y and the tangential lines 42 to the respectiveones of the contiguous portions 40 a, 40 b, and 40 c contiguous to theinner surface 14 of the cylinder 13.

In FIGS. 13 and 14, another four-cycle gasoline engine 1K serving as thereciprocating engine of another embodiment is comprised of the pistonring (top ring) 5 adjacent to the top surface 4 of the piston 3 definingthe combustion chamber 2; the piston ring (second ring) 7 which definesthe annular gas chamber 6 in cooperation with the piston ring 5 andwhich is adjacent to the piston ring 5 such that the pressure-receivingarea of the side surface 8 of the piston 3 in the annular gas chamber 6becomes greater on a swinging side surface portion 10K, which is locatedon the thrust side and opposes a swinging side surface portion 9Klocated on the counter-thrust side 9 of the piston 3, than on theswinging side surface portion 9K; the oil ring 16 which is locatedfurther away from the piston ring 5 on the swinging side surface portion10K side than on a substantially intermediate portion side between theswinging side surface portion 9K and the swinging side surface portion10K; and a recessed portion 15K serving as a gas passage which isdisposed in the inner surface 14 of the cylinder 13 and at a positionfor allowing the annular gas chamber 6 to communicate with thecombustion chamber 2 when the piston 3 is positioned in the vicinity ofthe top dead center.

Ring grooves, which are disposed in such a manner as to respectivelycorrespond to the piston rings 5 and 7 and the oil ring 16, are formedin the side surface 8 of the piston 3. The piston rings 5 and 7 and theoil ring 16 are respectively fitted in the ring grooves.

The connecting rod 22 is rotatably coupled at its small end portion tothe piston 3 through a connecting shaft (piston pin) 21. A crankshaft isrotatably coupled to a large end portion of the connecting rod.

The cylinder 13 has the cylinder bore (space) 25 defined by its innersurface, and the piston 3 is disposed in the cylinder bore 25 such thatthe piston 3 is reciprocatable in the reciprocating direction Y. Thecylinder 13 is provided with the ignition plug 26, an intake valve, andan exhaust valve 27K.

The piston ring 5 is fitted in the ring groove of the piston 3 such thatthe piston ring 5 is substantially parallel to the top surface (head endface) 4 of the piston 3 defining the combustion chamber 2.

The piston ring 7 is fitted in the ring groove of the piston 3 by beinginclined with respect to the reciprocating direction Y and the pistonring 5 so as to be located gradually away from the piston 3 as viewed inthe direction from the swinging side surface portion 9K toward theswinging side surface portion 10K. The distance from the piston ring 5to the piston ring 7 on the swinging side surface portion 10K side islonger than the distance from the piston ring 5 to the piston ring 7 onthe swinging side surface portion 9K side.

Abutment portions at respective both ends of the piston rings 5 and 7are closely abutted or fitted so that the gases will not leak throughthe abutment portions at these both ends.

The annular gas chamber 6 is defined by the side surface 8 of the piston3, the inner surface 14 of the cylinder 13, and the piston rings 5 and7.

A portion 31K which is substantially intermediate between the swingingside surface portions 9K and 10K of the oil ring 16 is disposed in sucha manner as to be spaced away from the piston ring S within a range inwhich it does not come into contact with the coupling shaft 21 in thereciprocating direction Y. A portion 32K located on the swinging sidesurface portion 10K side of the oil ring 16 is disposed in such a manneras to be further away from the piston ring 5 than the portion 31K in thereciprocating direction Y.

The recessed portion 15K is formed in the inner surface 14 facing theside surface 8 on the swinging side surface portion 10K side so as toallow the annular gas chamber 6 to communicate with the combustionchamber 2 in a case where the piston 3 is present at the position of thetop dead center and at a position corresponding to approximately 15degrees in terms of the crank angle.

A description will be given of the operation of the reciprocating engine1K of this embodiment. In the combustion stroke of the air-fuel mixturewhich is started after completion of the compression stroke, ignition bythe ignition plug 26 is effected while the piston 3 is positioned in thevicinity of the top dead center, and the combustion gases within thecombustion chamber 2 are introduced into the annular gas chamber 6through the recessed portion 15K. The piston 3 then receives the gaspressure of the combustion gases which heightened to a maximum while thepiston 3 is being positioned in the vicinity of the top dead centerafter the passage of the top dead center of the piston 3, so that-thepiston 3 accelerates toward the bottom dead center. Here, as a forwardmoving force is imparted from the forwardly moving piston 3 to theconnecting rod 22 which is tilted with respect to the reciprocatingdirection Y, a lateral pressure E1 which is directed toward the thrustside is imparted to the piston 3. However, a counter lateral pressure E2directed toward the counter-thrust side is imparted to the piston 3 bythe gas pressure within the annular gas chamber 6, thereby causing thepiston 3 to gas float.

In the reciprocating engine 1K constructed as described above, since thepiston 3 is brought to the position where the combustion chamber 2 andthe annular gas chamber 6 are communicated through the recessed portion15K during the combustion, the gas pressure which is generated throughcombustion in the combustion chamber 2 in the combustion stroke isspeedily introduced into the annular gas chamber 6 through the recessedportion 15K. Upon receiving the biased lateral pressure within theannular gas chamber 6 on the basis of this introduced gas pressure, thepiston 3 floats up (gas floats) with respect to the inner surface 14,particularly the inner surface 14 on the swinging side surface portion10K side, in its reciprocating motion. The piston 3 which is floated upby the gas pressure reciprocates with an extremely low slidingfrictional resistance. In addition, in such reciprocating motion,although the piston 3 tends to be swung (oscillated) about the couplingshaft 21 in D directions, this swinging motion is prevented by theaforementioned biased lateral pressure of the annular gas chamber 6. Thepiston 3 can thus be reciprocated with an extremely low slidingfrictional resistance without causing its side surface 8 on the swingingside surface portions 9K and 10K side to abut against the inner surface14 of the cylinder 13, thereby making it possible to attain animprovement and the like of the fuel consumption of the reciprocatingengine 1 K.

According to the reciprocating engine 1K of this embodiment, thereciprocating engine 1 has the oil ring 16 which is located further awayfrom the piston ring 5 on the swinging side surface portion 10K sidethan on a substantially intermediate portion side between the swingingside surface portion 9K and the swinging side surface portion 10K.Therefore, the oil ring 16 can be disposed such that the portion 31K ofthat oil ring 16 located above the coupling shaft 21 is located awayfrom the piston ring 5 within a range in which it does not interferewith the coupling shaft 21, and such that the portion 32K of that oilring 16 on the thrust side is located further way from the piston ring 5than the portion 31K. Hence, the piston ring 7 can be inclined greatlywith respect to the reciprocating direction Y without interfering withthe oil ring 16, such that the aforementioned pressure-receiving areabecomes greater on the swinging side surface portion 10K side than onthe swinging side surface portion 9K side. Thus, the piston 3 can befloated up (gas floated) from the inner surface 14 of the cylinder 13 bygenerating desired lateral pressure, thereby making it possible tosubstantially reduce the sliding frictional resistance between thecylinder 13 and the piston rings 5 and 7.

It should be noted that although in the above-described embodiments, thereciprocating engine is implemented as the four-cycle gasoline engines 1and 1K, the present invention is not limited to the same, andoperational effects similar to those described above can be obtained ifthe present invention is implemented as a diesel engine, for example.

1. A reciprocating engine comprising: a first piston ring adjacent to atop surface of a piston defining a combustion chamber; a second pistonring which defines an annular gas chamber in cooperation with said firstpiston ring and which is adjacent to said first piston ring such that apressure-receiving area of a side surface of said piston in said annulargas chamber becomes greater on a thrust side than on a counter-thrustside; and a plurality of gas passages which are disposed in an innersurface of a cylinder in such a manner as to be juxtaposed in acircumferential direction of the inner surface of said cylinder andwhich allow said annular gas chamber to communicate with said combustionchamber on the thrust side.
 2. The reciprocating engine according toclaim 1, wherein said plurality of gas passages respectively haverecessed portions which are disposed in the inner surface of saidcylinder at positions for allowing said annular gas chamber tocommunicate with said combustion chamber when said piston is at a topdead center or during a starting period of the fall from the top deadcenter.
 3. The reciprocating engine according to claim 2, wherein saidplurality of recessed portions are adapted to allow only said annulargas chamber to respectively communicate with said combustion chamber. 4.The reciprocating engine according to claim 2, wherein said plurality ofgas passages are disposed in the inner surface of said cylinder atpositions for allowing said annular gas chamber to communicate with saidcombustion chamber during the starting period of the fall of said pistonfrom the top dead center.
 5. The reciprocating engine according to claim2, wherein at least one of said recessed portions is disposed in theinner surface of said cylinder at a position for allowing said annulargas chamber to communicate with said combustion chamber when said pistonis positioned at the top dead center.
 6. The reciprocating engineaccording to claim 2, wherein said at least one of said recessedportions is disposed in such a manner as to be located further away froma cylinder head than other ones of said recessed portions concerning areciprocating direction.
 7. The reciprocating engine according to claim2, wherein said at least one of said recessed portions which is locatedmost away from a counter-thrust-side portion of said piston is disposedfurther away from said cylinder head than said other ones of saidrecessed portions concerning the reciprocating direction.
 8. Thereciprocating engine according to claim 2, wherein a center portion ofan opening plane of a space defined by said at least one of saidrecessed portions is disposed in such a manner as to oppose a centerportion of said piston concerning a direction which is perpendicular tothe reciprocating direction and an axial direction of a piston pin forcoupling said piston and a connecting rod.
 9. The reciprocating engineaccording to claim 6, wherein a portion located on a cylinder head sidein a contiguous portion, which is contiguous to the cylinder innersurface of said recessed portion disposed further away from saidcylinder head, is disposed closer to the cylinder head side thanportions of contiguous portions contiguous to the cylinder inner surfacein said other ones of said recessed portions and opposing in thereciprocating direction the portions thereof located on the cylinderhead side.
 10. The reciprocating engine according to claim 2, whereinone portions of the opening planes of the spaces respectively defined bysaid plurality of recessed portions are respectively positioned on aline extending in a circumferential direction.
 11. The reciprocatingengine according to claim 2, wherein there are provided a pair ofrecessed portions opposing each other concerning the axial direction ofsaid piston pin for coupling said piston and said connecting rod, and adistance from said cylinder head to one of said recessed portions in thereciprocating direction and a distance from said cylinder head to theother one of said recessed portions in the reciprocating direction aremutually equal.
 12. The reciprocating engine according to claim 2,wherein said plurality of recessed portions respectively have partiallyconcave spherical surfaces.
 13. The reciprocating engine according toclaim 2, wherein an intersection angle between a line extending in thereciprocating direction and a tangential line to said contiguous portioncontiguous to the cylinder inner surface in said at least one of saidrecessed portions is an obtuse angle.
 14. The reciprocating engineaccording to claim 2, wherein tangential lines to both portions opposingeach other in the reciprocating direction in said contiguous portioncontiguous to the cylinder inner surface in said at least one of saidrecessed portions intersect each other at a position located furtheraway from said piston than said both portions.
 15. The reciprocatingengine according to claim 2, wherein a line extending in thereciprocating direction and a tangential line to said contiguous portioncontiguous to the cylinder inner surface in said at least one of saidrecessed portions are perpendicular to each other.
 16. The reciprocatingengine according to claim 2, wherein said at least one of said recessedportions has a depth different from that of said recessed portionadjacent to that recessed portion in the circumferential direction. 17.The reciprocating engine according to claim 2, wherein said at least oneof said recessed portions is deeper than said other ones of saidrecessed portions located on the counter-thrust side relative to saidrecessed portion concerning the direction which is perpendicular to thereciprocating direction and the axial direction of said piston pin forcoupling said piston and said connecting rod.
 18. The reciprocatingengine according to claim 2, wherein said at least one of said recessedportions has a depth equal to that of said recessed portion adjacent tothat recessed portion in the circumferential direction.
 19. Thereciprocating engine according to claim 2, wherein there are provided apair of recessed portions opposing each other concerning the axialdirection of said piston pin for coupling said piston and saidconnecting rod, and an intersection angle between a line extending inthe axial direction and a line connecting the center portion of saidpiston and the center portion of the opening plane of the space definedby said one of said recessed portions and an intersection angle betweenthe line extending in the axial direction and a line connecting thecenter portion of said piston and the center portion of the openingplane of the space defined by said other one of said recessed portionsare mutually equal.
 20. The reciprocating engine according to claim 19,wherein said pair of recessed portions have mutually similar shapes. 21.The reciprocating engine according to claim 2, wherein an intervalbetween said both portions opposing each other in the reciprocatingdirection in each of said contiguous portions of said plurality ofrecessed portions contiguous to the inner surface of said cylinder isgreater than a thickness of said first piston ring.
 22. Thereciprocating engine according to claim 2, wherein an interval betweensaid both portions opposing each other in the reciprocating direction ineach of said contiguous portions of said plurality of recessed portionscontiguous to the inner surface of said cylinder is shorter than adistance in the reciprocating direction from a thrust-side portion of adefining surface of said first piston ring defining said annular gaschamber to a thrust-side portion of a defining surface of said secondpiston ring defining said annular gas chamber.
 23. The reciprocatingengine according to claim 2, wherein the opening plane of the spacedefined by said at least one of said recessed portions has a diameterdifferent from the opening plane of said space defined by said other oneof said recessed portions.
 24. The reciprocating engine according toclaim 2, wherein the opening plane of the space defined by said at leastone of said recessed portions has a diameter longer than the openingplane of said space defined by said recessed portion located closer tothe counter-thrust side relative to said recessed portion concerning thereciprocating direction and the axial direction of said piston pin forcoupling said piston and said connecting rod.
 25. The reciprocatingengine according to claim 2, wherein there are provided a pair ofrecessed portions opposing each other concerning the axial direction ofsaid piston pin for coupling said piston and said connecting rod, andthe diameter of the opening plane of the space defined by each of saidpair of recessed portions and the diameter of the opening plane of thespace defined by another recessed portion adjacent to said pair ofrecessed portions in the circumferential direction are mutuallydifferent.
 26. The reciprocating engine according to claim 2, whereinthe opening plane of the space defined by said at least one of saidrecessed portions has a diameter equal to that of the opening plane ofsaid space defined by another one of said recessed portions.
 27. Thereciprocating engine according to claim 1, wherein the defining surfacesaid first piston ring defining said annular gas chamber is disposed soas to be parallel to a plane perpendicular to the reciprocatingdirection.
 28. The reciprocating engine according to claim 2, whereinthe diameter of the opening plane of the space defined by said at leastone of said recessed portions is greater than a depth of that recessedportion.
 29. The reciprocating engine according to claim 1, wherein saidpiston ring is disposed in such a manner as to be inclined with respectto the reciprocating direction.
 30. The reciprocating engine accordingto claim 1, further comprising an oil ring disposed on said piston inface-to-face relation to said first piston ring with said second pistonring located therebetween, and a thrust-side portion of said oil ring islocated further away from said first piston ring than a portion of saidoil ring opposing said piston pin for coupling said piston and saidconnecting rod concerning the reciprocating direction.
 31. Thereciprocating engine according to claim 30, wherein said thrust-sideportion of said oil ring is located further away from said first pistonring than a counter-thrust-side portion of said oil ring.
 32. Thereciprocating engine according to claim 29, further comprising an oilring disposed on said piston in face-to-face relation to said firstpiston ring with said second piston ring located therebetween, and saidoil ring is disposed in such a manner as to be inclined with respect tothe reciprocating direction.
 33. The reciprocating engine according toclaim 32, wherein said oil ring and said second piston ring are disposedin such a manner as to be inclined with respect to the reciprocatingdirection with mutually equal angles.
 34. The reciprocating engineaccording to claim 1, wherein said piston pin for coupling said pistonand said connecting rod are off-centered toward the counter-thrust side.35. A reciprocating engine comprising: a first piston ring adjacent to atop surface of a piston defining a combustion chamber; a second pistonring which defines an annular gas chamber in cooperation with said firstpiston ring and which is adjacent to said first piston ring such that apressure-receiving area of a side surface of said piston in said annulargas chamber becomes greater on another swinging side surface portionopposing one swinging side surface portion of said piston than on saidone swinging side surface portion; an oil ring which is located furtheraway from said first piston ring on the other swinging side surfaceportion side than on a substantially intermediate portion side betweenthe one swinging side surface portion and the other swinging sidesurface portion; and a gas passage formed in at least one of said pistonand an inner surface of a cylinder and adapted to allow said annular gaschamber to communicate with said combustion chamber.
 36. Thereciprocating engine according to claim 35, wherein said second pistonring is disposed in such a manner as to be inclined with respect to areciprocating direction of said piston.
 37. The reciprocating engineaccording to claim 35, wherein said oil ring is disposed in such amanner as to be inclined with respect to a reciprocating direction ofsaid piston.
 38. The reciprocating engine according to claim 35, whereinsaid one swinging side surface portion is located on a counter-thrustside, and said other swinging side surface portion is located on athrust side.
 39. The reciprocating engine according to claim 35, whereinsaid gas passage is constituted by a recessed portion which is disposedin the inner surface of said cylinder at a position for allowing saidannular gas chamber to communicate with said combustion chamber whensaid piston is positioned at a top dead center.